Abstract
Purpose: :
The purpose of the present study was to determine whether neutral density filters cause differential suppression of swept spatial frequency VEP (sVEP) responses in normal versus amblyopic eyes.
Methods: :
sVEP was performed using both grating and vernier stimuli in 12 amblyopic subjects ages 8-17 (mean 11.0 +/- 2.7, 5 males) and 13 visually and neurologically normal subjects, ages 8-17 (mean 12.4 +/- 3.2, 6 males). Subjects were tested both with and without a 2.0 log u neutral density filter in front of each eye.
Results: :
Interocular acuity difference in amblyopes ranged from 0.20-0.51 LogMAR (mean 0.34 +/- 0.12). Neutral density filtration caused significantly greater depression of subjective Snellen visual acuity in normal as opposed to amblyopic fellow eyes (p < 0.001). Although 9/12 amblyopic subjects demonstrated significant suprathreshold interocular differences between the normal and amblyopic eyes for either grating or vernier stimuli in the unfiltered state, only 1 of these 9 subjects still demonstrated a significant interocular sVEP difference when each eye was filtered (p=0.0075), indicating preferential suppression of the normal eye. Suprathreshold sVEP responses were depressed by filtration in 8/12 amblyopic eyes as opposed to 13/13 right eyes of normal, 12/13 left eyes of normal subjects, and 12/12 normal fellow eyes of amblyopes (Fisher’s exact test, p = 0.039, 0.16, 0.093, respectively). Differential suppression in normal versus amblyopic eyes by neutral density filters was similar for both vernier and grating stimuli
Conclusions: :
Prior observations have demonstrated that neutral density filters cause differential depression of subjective visual acuity in normal as opposed to amblyopic eyes. Our study demonstrated that neutral density filtration also preferentially depresses suprathreshold sVEP responses in normal as opposed to amblyopic eyes. These data suggest that suprathreshold sVEP may be useful for the objective detection of amblyopia in preverbal or developmentally delayed subjects.
Keywords: amblyopia • electrophysiology: clinical • visual development: infancy and childhood